1. Field of the Invention
The present invention relates to a method of erasing radiation image information which remains on a stimulable phosphor sheet the cycle time for executing radiation image information recording and reading processing can be shortened by, for example, erasing only that radiation image information area on a long stimulable phosphor sheet which is actually subjected to radiation exposure.
2. Description of the Related Art
There has recently been proposed a radiation image information recording and reproducing system wherein the radiation-transmitted image of an object such as a human body is produced using a stimulable phosphor to obtain radiation image information that is temporarily stored and recorded on a stimulable phosphor or sheet, and the stimulable phosphor sheet is scanned with exciter rays to emit accelerated light for photoelectrically reading the emitted light so as to produce an image signal that is electrically processed for generating radiation image information of the object appropriate to the diagnosis (see Japanese Patent Application Laid-Open Nos. 55-12429, 56-11395, 55-163472, 56-104645, 55-116340, etc.).
In the radiation image information recording and reproducing system, a final image may be reproduced as a hard copy or may be reproduced as a visible image on a CRT. According to the radiation image information recording and reproducing system referred to above, the stimulable phosphor sheet is used to temporarily bear image information in order to apply the above final image to a recording medium without finally recording image information on the stimulable phosphor sheet. Therefore, the stimulable phosphor sheet referred to above may be repeatedly used, and hence the repetitive use of the stimulable phosphor sheet permits considerable economies.
As described above, the reuse of the stimulable phosphor sheet is performed in the following manner. Namely, the energy of radiation, which remains on the stimulable phosphor sheet after the accelerated light emitted therefrom is read, is discharged by a method described in Japanese Patent Application Laid-Open Nos. 56-11392 and 56-12599, for example, so as to erase remaining or residual radiation image information. Thereafter, such a stimulable phosphor sheet may be used again to record the radiation image information.
There has already been proposed by the present applicant a so-called built-in type radiation image information recording and reading apparatus of such a type that a circulating feed means for feeding a stimulable phosphor sheet capable of storing and recording a radiation image thereon along a predetermined circulating passage, an image recording unit disposed on the circulating passage, for exposing the stimulable phosphor sheet to a radiation having image information to store and record radiation-transmitted image information of an object on the stimulable phosphor sheet, an image reading unit disposed on the circulating passage and comprising an exciter light source for generating exciter rays used to scan the stimulable phosphor sheet on which the radiation-transmitted image information of the object is stored and recorded in the image recording unit and a photoelectric reading means for photoelectrically reading accelerated light emitted from the stimulable phosphor sheet scanned with the exciter rays so as to produce an image signal, and an erasing unit disposed on the circulating passage, for discharging the radiation energy which remains on the stimulable phosphor sheet before the image recording is made to a stimulable phosphor sheet after the image reading is performed in the image reading unit, are all incorporated into a single apparatus, and the stimulable phosphor sheet is caused to circulate among the respective units mentioned above so as to be repeatedly used (see Japanese Patent Application Laid-Open No. 59-192240).
The radiation image information recording and reading apparatus having such a structure is advantageous in that the recording and reading of the radiation image information can continuously and efficiently be carried out.
The built-in type radiation image information recording and reading apparatus is intended to record a radiation-transmitted image of the chest, the abdomen, the limbs or the like of a patient. The stimulable phosphor sheet used to record the same is selected so as to be the same size as predetermined film formats (for example, a film format of 354 mm.times.430 mm or greater) corresponding to the images of these parts of the patient to be recorded.
There has recently been demand for the diagnosis of the whole length of the spine (a so-called diagnosis of all the vertebrae) using the built-in type radiation image information recording and reading apparatus. It is therefore convenient if a long stimulable phosphor sheet having the length corresponding to the full length of the spine to be recorded is used when the diagnosis of the whole spine is performed using the built-in type radiation image information recording and reading apparatus.
It is desirable that the built-in type radiation image information recording and reading apparatus using the long stimulable phosphor sheet is employed even in the exposure of the chest, the abdomen, the limbs or the like as well as in the exposure of the whole spine in order to improve the rate of operation of the apparatus or the like. In this case, an image is recorded only on a part of the stimulable phosphor sheet, which corresponds in size to a part subjected to exposure.
However, the above-described erasing method which has been employed in the above-mentioned conventional apparatus has the problem in that since the erasing of the radiation image information from the stimulable phosphor sheet is always made to the overall recording area of the stimulable phosphor sheet, that is, the full area, the unnecessary time taken for the, erasure of an image-unrecorded area on the long stimulable phosphor sheet is made where the radiation image information is recorded only on a part of the long stimulable phosphor sheet and the erasure of the residual image information with respect to the part thereof is performed over its full area, thereby resulting in a considerable increase in the cycle time required to record, read and erase the radiation image information.